Shelbs.

sciencecenter:

The oddest mating ritual you’ll watch today, guaranteed

Male mountain goats compete over mates by ramming each other with their horns. Many alpha mammals chase away lesser males. Human males wear Axe and posture in bars. But flatworms might take mating competition to the furthest extreme. They engage in something called “penis fencing,” in which two flatworms try to stab each other with their, er, swords. The first to puncture the other and deliver its semen payload wins. Be sure to check out the video.

Penis Fencing……I have heard it all now